Electric power tool

ABSTRACT

An electric power tool includes: a brushless motor having a plurality of stator windings and configured to rotate in accordance with voltages applied to the plurality of stator windings, an induced voltage being generated in accordance with a rotation of the brushless motor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to smooth the AC voltage rectified by the rectifier circuit to a pulsation voltage having a maximum value larger than the induced voltage and a minimum value smaller than the induced voltage; and an inverter circuit configured to perform switching operations to output the pulsation voltage to the plurality of stator windings by rotation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/882,073, filed Apr. 26, 2013, which claims priorities from JapanesePatent Application Nos. 2011-060932, 2011-060833, and 2011-060901, thosefiled Mar. 18, 2011. The entire contents of the above noted applicationsare incorporated herein by reference. Incidentally, the U.S. applicationSer. No. 13/882,073 is entered into U.S. national phase fromInternational Application No. PCT/JP2012/001898 filed Mar. 19, 2012 inJapan Patent Office as a Receiving Office, which claims the abovedescribed priorities.

TECHNICAL FIELD

The invention relates to an electric power tool.

BACKGROUND

Japanese Patent Publication No. 4487836 discloses an electric devicethat controls a motor with an inverter circuit to operate an end toolconnected to the motor.

SUMMARY

Because the above conventional electric power tool includes a smoothingcapacitor having large capacity, power factor of AC power isdeteriorated.

Further, in order to improve the power factor, an electric power toolequipping with a power-factor improvement circuit can be also conceived.However, such configuration increases the size of the electric powertool and increases the cost.

In view of the foregoing, it is an object of the invention to provide anelectric power tool capable of improving power factor without equippingwith a power-factor improvement.

In order to attain the above and other objects, the invention providesan electric power tool including: a brushless motor having a pluralityof stator windings and configured to rotate in accordance with voltagesapplied to the plurality of stator windings, an induced voltage beinggenerated in accordance with a rotation of the brushless motor; arectifier circuit configured to rectify an AC voltage; a smoothingcapacitor configured to smooth the AC voltage rectified by the rectifiercircuit to a pulsation voltage having a maximum value larger than theinduced voltage and a minimum value smaller than the induced voltage;and an inverter circuit configured to perform switching operations tooutput the pulsation voltage to the plurality of stator windings byrotation.

It is preferable that the electric power tool further includes: areceiving unit configured to receive an instruction for the invertercircuit to perform the switching operations; and a control unitconfigured to control the inverter circuit to continue to perform theswitching operations while the receiving unit is receiving theinstruction, even if the pulsation voltage is smaller than the inducedvoltage.

It is preferable that the control unit prevents the inverter circuitfrom performing the switching operations when a current flowing throughthe brushless motor is larger than an overcurrent threshold.

Another aspect of the present invention provides an electric power toolincluding: a brushless motor including: a stator having a plurality ofstator windings to which an AC voltage is applied from an AC powersource; and a rotor rotatable for the stator; an end tool (designated byreference numeral 1 a in FIG. 1) that is driven in accordance with therotation of the rotor; an inverter circuit configured to performswitching operations to output the pulsation voltage to the plurality ofstator windings by rotation, even if the AC voltage is smaller than apreset voltage.

Another aspect of the present invention provides an electric power toolincluding: a motor; a voltage supplying unit configured to supply adrive voltage to the motor; a current detecting circuit configured todetect a current flowing through the motor; and a control unitconfigured to control the voltage supplying unit to decrease the drivevoltage when the current detected by the current detecting circuit islarger than a first current.

It is preferable that the control unit controls the voltage supplyingunit to stop supplying the drive voltage when the current detected bythe current detecting circuit is larger than a second current largerthan the first current.

It is preferable that the voltage supplying unit supplies a pulsationvoltage including a plurality of ripples as the drive voltage to themotor. The current detecting circuit detects a peak of the currentflowing through the motor. The control unit controls the voltagesupplying unit to decrease the drive voltage when the peak detected bythe current detecting circuit is larger than the first current, keep thedecreased drive voltage until a next peak is detected, and increases thedecreased drive voltage stepwise if the next peak is smaller than thefirst current.

It is preferable that the voltage supplying unit includes an invertercircuit.

Another aspect of the present invention provides an electric power toolincluding: a motor; a voltage supplying unit configured to supply adrive voltage set to a target voltage to the motor; a rotational speeddetecting circuit configured to detect a rotational speed of the motor;and a control unit configure to change the target voltage based on therotational speed detected by the rotational speed detecting unit.

Another aspect of the present invention provides an electric power toolincluding: a power cable connectable to an AC power source; a brushlessmotor that is rotated with a power supplied from the AC power source; anend tool that is driven in accordance with the rotation of the brushlessmotor; a current detecting circuit configured to detect a currentflowing through the brushless motor; and a control unit configured todecrease a drive voltage of the brushless motor when the currentdetected by the current detecting circuit is larger than a presetcurrent value.

It is preferable that the control unit gradually decreases the drivevoltage when the current detected by the current detecting circuit islarger than the preset current value.

It is preferable that the control unit performs a PWM control todecrease the drive voltage. The control unit performs the PWM controlwith a duty smaller than 100% when the current detected by the currentdetecting circuit is larger than the preset current value. The controlunit performs the PWM control with a duty of 100% when the currentdetected by the current detecting circuit is smaller than the presetcurrent value.

Another aspect of the present invention provides an electric power toolincluding: a power cable connectable to an AC power source; a brushlessmotor that is rotated with an AC power supplied from the AC powersource, a pulsation current flowing through the brushless motor with theAC power; an end tool that is driven in accordance with the rotation ofthe brushless motor; a current detecting circuit configured to detectthe pulsation current flowing through the brushless motor; and arestraining unit configured to retrain a peak of the pulsation currentflowing through the brushless motor.

It is preferable that the restraining unit performs a PWM control toretrain a peak of the pulsation current flowing through the brushlessmotor.

Another aspect of the present invention provides an electric power toolincluding: a motor; a voltage supplying unit configured to generate adrive voltage from a DC voltage and supply the drive voltage to themotor; a voltage detecting circuit configured to detect the DC voltage;and a control unit configured to prohibit the voltage supplying unitfrom supplying the drive voltage to the motor when the DC voltagedetected by the voltage detecting circuit is outside a preset range.

Another aspect of the present invention provides an electric power toolincluding: a motor; a rectifier circuit configured to convert an ACvoltage into a rectified voltage; a voltage supplying unit configured togenerate a drive voltage from the rectified voltage and supply the drivevoltage to the motor; a voltage detecting circuit configured to detectthe rectified voltage; and a control unit configured to prohibit thevoltage supplying unit from supplying the drive voltage to the motorwhen the rectified voltage detected by the voltage detecting circuit isoutside a preset range.

It is preferable that the voltage detecting circuit detects a peak ofthe rectified voltage. The control unit prohibits the voltage supplyingunit from supplying the drive voltage to the motor when the rectifiedvoltage detected by the voltage detecting circuit is outside the presetrange.

Another aspect of the present invention provides an electric power toolincluding: a power cable connectable to an AC power source; a voltagesupplying unit configured to generate a drive voltage from the powersupplied from the AC power source; a brushless motor that is rotatedwith the drive voltage; an end tool that is driven in accordance withthe rotation of the brushless motor; a current detecting circuitconfigured to detect a current flowing through the brushless motor; anda control unit configured to perform a PWM control to control thevoltage supplying unit. The control unit determines a duty of the PWMcontrol based on a difference between the current detected by thecurrent detecting circuit and a first current value when the currentdetected by the current detecting circuit is larger than the firstcurrent value.

Another aspect of the present invention provides an electric power toolincluding: a power cable connectable to an AC power source; a voltagesupplying unit configured to generate a drive voltage from the powersupplied from the AC power source; a brushless motor that is rotatedwith the drive voltage; an end tool that is driven in accordance withthe rotation of the brushless motor; a current detecting circuitconfigured to detect a current flowing through the brushless motor; anda control unit configured to perform a PWM control to control thevoltage supplying unit. The control unit decreases a duty of the PWMcontrol when the drive voltage is larger than a first voltage value.

Another aspect of the present invention provides an electric power toolincluding: a power cable connectable to an AC power source; a voltagesupplying unit configured to generate a drive voltage from the powersupplied from the AC power source; a brushless motor that is rotatedwith the drive voltage; an end tool that is driven in accordance withthe rotation of the brushless motor; a voltage detecting circuitconfigured to detect the drive voltage; and a control unit configured toperform a PWM control to control the voltage supplying unit. The controlunit determines a duty of the PWM control based on a difference betweenthe voltage detected by the voltage detecting circuit and a firstvoltage value when the voltage detected by the voltage circuit is largerthan the first voltage value.

BRIEF DESCRIPTION OF THE DRAWINGS

The particular features and advantages of the disclosure as well asother objects will become apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of an electric power tool according to afirst embodiment of the present invention;

FIG. 2 is an explanation diagram of pulsation voltages includingripples;

FIG. 3 is a diagram showing change of current when a smoothing capacitorhaving small capacitor is used;

FIG. 4 is a diagram showing current paths for operations of an invertercircuit according to the first embodiment of the present invention;

FIG. 5 is a diagram showing change of current when the inverter circuitis stopped;

FIG. 6 is a diagram showing a relationship between current flowingthrough a motor and rectified voltage;

FIG. 7 is a diagram showing thresholds for peak voltage of AC voltage;

FIG. 8 is a flowchart of a prohibiting control according to a secondembodiment of the present invention;

FIG. 9 is a diagram showing a relationship between voltage and targetduty;

FIG. 10 is a diagram showing a control according to the secondembodiment of the present invention;

FIG. 11 is a circuit diagram of an electric power tool according to afirst modification of the second embodiment of the present invention;

FIG. 12 is a circuit diagram of an electric power tool according to asecond modification of the second embodiment of the present invention;

FIG. 13 is a diagram showing a relationship between load and current;

FIG. 14 is a diagram showing a control according to a third embodimentof the present invention;

FIG. 15 is a flowchart of the control according to the third embodimentof the present invention;

FIG. 16 is a diagram showing a relationship between a target duty and arotational speed when a control according to a fourth embodiment of apresent invention is performed;

FIG. 17 is a diagram showing the control according to the fourthembodiment of the present invention;

FIG. 18 is a flowchart of the control according to the fourth embodimentof the present invention;

FIG. 19 is a diagram showing waveform of current when a controlaccording to the third embodiment is performed for AC power;

FIG. 20 is a diagram showing a control according to a fifth embodimentof the present invention;

FIG. 21 is a flowchart of the control according to the fifth embodimentof the present invention;

FIG. 22 is a diagram showing a control according to a sixth embodimentof the present invention; and

FIG. 23 is a flowchart of the control according to the sixth embodimentof the present invention.

DETAILED DESCRIPTION

Hereinafter, an electric power tool 1A according to a first embodimentof the invention will be described while referring to FIGS. 1 through 5.

FIG. 1 is a circuit diagram of the electric power tool 1A according tothe first embodiment. As shown in FIG. 1, the electric power tool 1Aincludes a trigger switch (the receiving unit of the present invention)3, a control-circuit-voltage supplying circuit (referred as “CVS” inFIG. 1) 4, a motor 5, rotor-position detecting elements 6, a controller7, an inverter circuit (the inverter circuit and the voltage supplyingunit of the present invention) 8, a normal-mode filter 9, a rectifiercircuit 10, and a smoothing capacitor 11.

When the trigger switch 3 is operated, AC voltage outputted from acommercial power source 2 is rectified and smoothed by the rectifiercircuit 10 and the smoothing capacitor 11, and is supplied to the motor5 via the inverter circuit 8. Further, when the trigger switch 3 isoperated, the control-circuit-voltage supplying circuit 4 generates acontrol-circuit driving voltage (15V in the present embodiment) andsupplies the control-circuit driving voltage to the controller 7.

The motor 5 is a three-phase brushless DC motor, and includes a rotor 5Aand a stator 5B. The rotor 5A is made of a permanent magnet including aplurality of sets (two sets in the present embodiment) of N poles and Spoles. The stator 5B is made of three-phase stator windings U, V, and Wthat are connected by star connection. The motor 5 (the rotor 5A)rotates by sequentially switching the stator windings U, V, and Wthrough which current flows. Switching of the stator windings U, V, andW will be described later.

The rotor-position detecting elements 6 are arranged at positionsconfronting the permanent magnet of the rotor 5A with a predeterminedinterval (for example, an angle of 60 degrees) in the circumferentialdirection of the rotor 5A. The rotor-position detecting elements 6output a signal in accordance with rotational position of the rotor 6A.

The controller 7 includes a motor-current detecting circuit (the currentdetecting unit of the present invention) (referred as “MCD” in FIG. 1)71, a rectified-voltage detecting circuit (the voltage detecting unit ofthe present invention) (referred as “RVD” in FIG. 1) 72, acontrol-circuit-voltage detecting circuit (referred as “CVD” in FIG. 1)73, a switch-operation detecting circuit (referred as “SOD” in FIG. 1)74, an applied-voltage setting circuit (referred as “AVS” in FIG. 1) 75,a rotor-position detecting circuit (referred as “RPD” in FIG. 1) 76, amotor-rotational-speed detecting circuit (the rotational speed detectingunit of the present invention) (referred as “RSD” in FIG. 1) 77, anarithmetic section (the control unit of the present invention) 78, acontrol-signal outputting circuit (referred as “CSO” in FIG. 1) 79, andan AC-input-voltage detecting circuit (referred as “AVD” in FIG. 1) 80.

The AC-input-voltage detecting circuit 80 detects a peak value of ACvoltage outputted from the commercial power source 2, and outputs thepeak value to the arithmetic section 78. In the present embodiment, ACvoltage is detected in a sampling period that a value sufficiently closeto the actual peak value can be detected.

The motor-current detecting circuit 71 detects current supplied to themotor 5, and outputs the current to the arithmetic section 78. Therectified-voltage detecting circuit 72 detects voltage outputted fromthe rectifier circuit 10 and the smoothing capacitor 11, and outputs thevoltage to the arithmetic section 78. The control-circuit-voltagedetecting circuit 73 detects control-circuit driving voltage suppliedfrom the control-circuit-voltage supplying circuit 4, and outputs thedriving voltage to the arithmetic section 78. The switch-operationdetecting circuit 74 detects whether the trigger switch 3 is operated,and outputs the detection result to the arithmetic section 78. Theapplied-voltage setting circuit 75 detects operation amount of thetrigger switch 3, and outputs the operation amount to the arithmeticsection 78.

The rotor-position detecting circuit 76 detects rotational position ofthe rotor 6A based on signals from the rotor-position detecting elements6, and outputs the rotational position to the motor-rotational-speeddetecting circuit 77 and the arithmetic section 78. Themotor-rotational-speed detecting circuit 77 detects rotational speed ofthe rotor 6A based on signals from the rotor-position detecting circuit76, and outputs the rotational speed to the arithmetic section 78.

The arithmetic section 78 generates switching signals H1-H6 based onsignals from the rotor-position detecting circuit 76 and from themotor-rotational-speed detecting circuit 77, and outputs the switchingsignals H1-H6 to the control-signal outputting circuit 79. Further, thearithmetic section 78 adjusts switching signals H4-H6 as pulse widthmodulation signal (PWM signal) based on signals from the applied-voltagesetting circuit 75, and outputs the PWM signal to the control-signaloutputting circuit 79. The switching signals H1-H6 are outputted to theinverter circuit 8 via the control-signal outputting circuit 79. Notethat the controller 7 may be so configured to adjust the switchingsignals H1-H3 as PWM signals.

The inverter circuit 8 includes switching elements Q1-Q6. Each gate ofthe switching elements Q1-Q6 is connected with the control-signaloutputting circuit 79, and each drain or source of the switchingelements Q1-Q6 is connected with the stator windings U, V, and W of thestator 5B.

The switching elements Q1-Q6 performs switching operations based on theswitching signals H1-H6 inputted from the control-signal outputtingcircuit 79, changes DC voltage of the battery pack 20 applied to theinverter circuit 8 into three-phase (U-phase, V-phase, and W-phase)voltages Vu, Vv, and Vw, and supplies the three-phase voltages Vu, Vv,and Vw to the stator windings U, V, and W, respectively.

Specifically, the switching signals H1-H6 are inputted to the switchingelements Q1-Q6, respectively. With this operation, the energized statorwindings U, V, and W, that is, the rotational direction of the rotor 5Ais controlled. At this time, amount of electric power supplied to thestator windings U, V, and W is controlled with the switching signalsH4-H6 which are also PWM signals.

With the above-described configuration, the electric power tool 1A cansupply the motor 5 with driving voltage in accordance with the operationamount of the trigger switch 3.

Here, because a conventional electric power tool includes a smoothingcapacitor having large capacity, power factor of AC power isdeteriorated. Further, in order to improve the power factor, aconfiguration equipping with a power-factor improvement circuit can bealso conceived. However, such configuration increases the size of thepower tool and increases the cost.

On the other hands, a smoothing capacitor having small capacity cannotcompletely smooth AC voltage outputted from the rectifier circuit 10. Asthe result, pulsation voltage including ripples (for example, FIG. 2(b))is outputted from the smoothing capacitor.

When the motor 5 is rotated, induced voltage is generated in the motor5. In order to the motor 5, it is required to apply voltage larger thanthe induced voltage to the motor 5. Thus, if the pulsation voltage isapplied to the motor 5, the motor 5 cannot be driven in a section Y(FIG. 3) where the magnitude of the pulsation voltage is smaller thanthe induced voltage. That is, as shown in FIG. 4(a), current flows inthe electric power tool 1A in a section X where the magnitude of thepulsation voltage is larger than or equal to the induced voltage. Incontrast, as shown in FIG. 4(b), current does not flow in the electricpower tool 1A in the section Y where the magnitude of the pulsationvoltage is smaller than the induced voltage.

However, the electric power tool 1A according to the present embodimentuses the smoothing capacitor 11 having small capacity, by design, thatoutputs pulsation voltage having maximum voltage larger than the inducedvoltage and minimum voltage smaller than the induced voltage to generatethe section Y. Hereinafter, the reason why the electric power tool 1Aaccording to the present embodiment uses the smoothing capacitor 11having small capacity will be described.

FIG. 2(a) shows voltage waveforms in which ripples are 100%, FIG. 2(b)shows voltage waveforms in which ripples are 50%, and FIG. 2(c) showsvoltage waveforms in which ripples are 0%. As shown in FIG. 2, the ratioof ripples decreases as the capacity of the smoothing capacitor 11increases. In the present embodiment, the capacity of the smoothingcapacitor 11 is determined based on both this relationship (between theratio of ripples and the capacity of the smoothing capacitor 11) and theinduced voltage. Hereinafter, a case will be described in whichpulsation voltage including ripples of 100% is outputted from thesmoothing capacitor 11.

As described above, current does not flow in the electric power tool 1Ain the section Y. However, if the motor 5 is once driven in the sectionX, the motor 5 can continue rotating in the section Y due to inertia.Therefore, if the motor 5 is cyclically driven in the section X, themotor 5 can continue rotating even if not driven in the section Y.Hence, the electric power tool 1A according to the present embodimentcan improve the power factor without equipping with the power-factorimprovement circuit with the smoothing capacitor 11 having smallcapacity that outputs pulsation voltage having maximum voltage largerthan the induced voltage and minimum voltage smaller than the inducedvoltage to generate the section Y.

Further, for saving energy, a control that stops operations of theinverter circuit 8 in the section Y where the magnitude of pulsationvoltage is smaller than the induced voltage is conceivable.

However, if the inverter circuit 8 is stopped in the section Y, energystored in the stator windings U, V, and W of the motor 5 flows reverselytoward the smoothing capacitor 11 (FIG. 4(c)) in a section Z (FIG. 5)that is immediately after the inverter circuit 8 is stopped. As aresult, voltage of the smoothing capacitor 11 increases rapidly, whichcan cause damage and deterioration of quality of the smoothing capacitor11.

Hence, in the present embodiment, while the trigger switch 3 isoperated, the inverter circuit 8 is controlled not so as to stopoperations even in the section Y where the magnitude of pulsationvoltage is smaller than the induced voltage. This control can preventenergy stored in the stator windings U, V, and W of the motor 5 fromflowing reversely toward the smoothing capacitor 11, and the voltage ofthe smoothing capacitor 11 from increasing rapidly. Hence, damage anddeterioration of quality of the smoothing capacitor 11 can be prevented.

However, the inverter circuit 8 may be controlled to stop operations ifcurrent detected by the motor-current detecting circuit 71 exceeds anovercurrent threshold.

Further, the above control that does not stop operations of the invertercircuit 8 while the trigger switch 3 is operated can be also used in aconstruction that does not equip with the smoothing capacitor 11.

Next, an electric power tool 1B according to a second embodiment of theinvention will be described while referring to FIGS. 6 through 10. Theelectric power tool 1B has an identical circuit configuration (FIG. 1)as the electric power tool 1A according to the first embodiment.Therefore, the descriptions of the circuit configuration are omitted.

The inverter circuit 8 needs to be driven by voltage within a usablerange R1 (FIG. 7) (for example, rectified voltage of approximately 110to 200V, effective value of AC input voltage of approximately 80 to120V, max (peak) value of AC input voltage of approximately 120 to140V). FIG. 6(a) shows a relationship between current flowing throughthe motor 5 and the rectified voltage outputted from the rectifiercircuit 10 at a normal condition. However, as shown in FIG. 6(b), ifcurrent flowing through the motor 5 is large, voltage generated from Lcomponent in the circuit can be superimposed onto the rectified voltageoutputted from the rectifier circuit 10. If this voltage does not fallwithin the usable range R1 of the inverter circuit 8, the invertercircuit 8 can be damaged.

Thus, the electric power tool 1B of the present embodiment prohibits(restricts) supplying of electric power to the motor 5, if voltageoutside a preset range R2 (FIG. 7) that falls into the usable range R1is supplied to the inverter circuit 8 (the arithmetic section 78).

For example, as shown in FIG. 7, if peak voltage V1 detected by theAC-input-voltage detecting circuit 80 falls into a prohibiting range R3that is less than or equal to a voltage threshold A (for example, 120V),or falls into a prohibiting range R4 is larger than or equal to avoltage threshold B (for example, 140V), the PWM duties of PWM signalsH4-H6 outputted to the switching elements Q4-Q6 are set to zero, therebyprohibiting supplying of electric power to the motor 5. Thus, failure ofthe inverter circuit 8 can be prevented.

Additionally, in the present embodiment, although not shown in figures,if rectified voltage V2 detected by the rectified-voltage detectingcircuit 72 is less than or equal to a voltage threshold C (for example,110V), or is larger than or equal to a voltage threshold D (for example,200V), supplying of electric power to the motor 5 is prohibited in orderto protect the inverter circuit 8.

Further, in the present embodiment, although not shown in figures, ifcontrol voltage V3 detected by the control-circuit-voltage detectingcircuit 73 is less than or equal to a voltage threshold E (for example,10V, not shown), or is larger than or equal to a voltage threshold F(for example, 20V, not shown), supplying of electric power to the motor5 is prohibited in order to protect the arithmetic section 78.

Here, the above-mentioned prohibiting control performed by thearithmetic section 78 will be described in detail while referring toFIG. 8. FIG. 8 is a flowchart of the prohibiting control according tothe present embodiment. The flowchart is started when a power switch(not shown) of the electric power tool 1B is turned on.

First, the arithmetic section 78 determines whether the peak voltage V1detected by the AC-input-voltage detecting circuit 80 is less than orequal to the voltage threshold A, or is larger than or equal to thevoltage threshold B (S101).

If the peak voltage V1 is less than or equal to the voltage threshold A,or is larger than or equal to the voltage threshold B (S101: Yes),target duty Dt of the PWM signals H4, H5, and H6 is set to 0%, therebyprohibiting supplying of electric power to the motor 5 (S102). Thisprevents supply of voltage outside the usable range R1 to the invertercircuit 8.

On the other hand, if the peak voltage V1 is larger than the voltagethreshold A and is less than the voltage threshold B (S101: No), thearithmetic section 78 then determines whether the rectified voltage V2detected by the rectified-voltage detecting circuit 72 is less than orequal to the voltage threshold C, or is larger than or equal to thevoltage threshold D (S103).

If the rectified voltage V2 is less than or equal to the voltagethreshold C, or is larger than or equal to the voltage threshold D(S103: Yes), the target duty Dt of the PWM signals H4, H5, and H6 is setto 0%, thereby prohibiting supplying of electric power to the motor 5(S102). This prevents supply of voltage outside the usable range to theinverter circuit 8.

On the other hand, if the rectified voltage V2 is larger than thevoltage threshold C and is less than the voltage threshold D (S103: No),the arithmetic section then determines whether the control voltage V3detected by the control-circuit-voltage detecting circuit 73 is lessthan or equal to the voltage threshold E, or is larger than or equal tothe voltage threshold F (S104).

If the control voltage V3 is less than or equal to the voltage thresholdE, or is larger than or equal to the voltage threshold F (S104: Yes),the target duty Dt of the PWM signals H4, H5, and H6 is set to 0%,thereby prohibiting supplying of electric power to the motor 5 (S102).This prevents supply of voltage outside the usable range to thearithmetic section 78.

If the control voltage V3 is larger than the voltage threshold E and isless than the voltage threshold F (S104: No), the arithmetic section 78then determines whether the trigger switch 3 is turned on (S105).

If the trigger switch 3 is not turned on (S105: No), the arithmeticsection 78 returns to S101. If the trigger switch 3 is turned on (S105:Yes), the arithmetic section 78 then determines whether the peak voltageV1 is larger than or equal to a voltage threshold G (S106).

Here, as shown in FIG. 7, if the peak voltage V1 falls into a preventionrange R5 that is smaller than the voltage threshold B and larger than orequal to a voltage threshold G (for example, 105V), the inverter circuit8 is not damaged at this time. However, in this range R5, the peakvoltage V1 can easily go out of the preset range R2 if current increasesor noises are generated.

Accordingly, in the present embodiment, if the peak voltage V1 is largerthan or equal to the voltage threshold G (S106: Yes), the arithmeticsection 78 sets the target duty Dt to a value less than 100% (S107) andreturns to S101. Specifically, as shown in FIG. 9, the arithmeticsection 78 sets the target duty Dt to a value indicated byDt=(V1/G)×100, and returns to S101. With this operation, as shown inFIG. 10, if the peak voltage V1 is larger than or equal to the voltagethreshold G, voltage supplied to the inverter circuit 8 and thearithmetic section 78 can be reduced.

Further, generally, if current increases, voltage also increases due tothe effect of L component of the circuit. However, by decreasing theduty as described above, current is also decreased. Therefore, rise ofrectified voltage can be also prevented.

As to the rectified voltage V2, by performing a similar control if therectified voltage V2 is larger than or equal to a voltage threshold H(for example, 170V) as well, voltage supplied to the inverter circuit 8and the arithmetic section 78 can be reduced. This can preventincreasing of the rotational speed of the motor increases due to highvoltage input, which causes mechanical damages in a mechanical sectionand a motor section.

On the other hand, if the peak voltage V1 is less than the voltagethreshold G (S106: No), the arithmetic section 78 sets the target dutyDt to 100% (S108) and returns to S101 because the peak voltage V1 fallsinto a normal range R6.

In this way, in the electric power tool 1B of the present embodiment,the preset range R2 that falls into the usable range R1 is set, andsupplying of electric power to the motor 5 is prohibited if voltageoutside the preset range R2 is supplied to the inverter circuit 8 (thearithmetic section 78). This can prevent supply of voltage outside theusable range R1 the inverter circuit 8 (the arithmetic section 78),thereby preventing fail of the inverter circuit 8 (the arithmeticsection 78).

Further, in the electric power tool 1B of the present embodiment, in astate where the motor 5 is driven, if voltage supplied to the invertercircuit 8 (the arithmetic section 78) falls into the preset range R2 butis outside the normal range R6, that is, voltage falls into theprevention range R5, a control for reducing the voltage is performed.This can prevent supply of voltage outside the usable range is suppliedto the inverter circuit 8 (the arithmetic section 78).

Note that although, in the above-described embodiment, AC power from thecommercial power source 2 is converted into DC power, and then issupplied to the inverter circuit 8, DC power from the battery pack 20may be directly supplied to the inverter circuit 8, as shown in FIG. 11.In this case, a battery-voltage detecting circuit (the voltage detectingunit of the present invention) (referred as “BVD” in FIG. 11) 81 isprovided instead of the rectified-voltage detecting circuit 72 shown inFIG. 1. And, if voltage detected by the battery-voltage detectingcircuit 81 or voltage detected by the control-circuit-voltage detectingcircuit 73 is outside the preset range, supply of electric power to themotor 5 is prohibited.

Further, in order to boost the voltage of the battery pack 20, as shownin FIG. 12, a configuration is conceivable that a boost-circuit-voltagesupplying circuit (referred as “BVS” in FIG. 11) 40 and aboost-circuit-voltage detecting circuit (referred as “BVC” in FIG. 11)82 are provided, instead of the control-circuit-voltage supplyingcircuit 4 and the control-circuit-voltage detecting circuit 73 shown inFIG. 11. In this configuration, voltage boosted by theboost-circuit-voltage supplying circuit 40 is supplied to the arithmeticsection 78. In this configuration, if voltage detected by thebattery-voltage detecting circuit 81 or voltage detected by theboost-circuit-voltage detecting circuit 82 is outside the preset range,supply of electric power to the motor 5 is prohibited.

Further, although in the above embodiment, prohibition of supplying ofelectric power to the motor 5 is determined for each voltage at aplurality of locations. However, prohibition of supplying of electricpower to the motor 5 may be determined based on a voltage at any one ofthe plurality of locations.

Next, an electric power tool 1C according to a third embodiment of theinvention will be described while referring to FIGS. 13 through 15. Theelectric power tool 1C has an identical circuit configuration (FIG. 1)as the electric power tool 1A according to the first embodiment.Therefore, the descriptions of the circuit configuration are omitted.

As shown in FIG. 13, current flowing through the motor 5 is proportionalto load applied to the motor 5. The motor 5 can be damaged when greatcurrent flows through the motor 5 (great load is applied on the motor5).

Thus, as shown in FIG. 14, the electric power tool 1C according to thethird embodiment performs a control for setting a target current Itsmaller than an overcurrent threshold Ith, and decreasing PWM duties ofthe PWM signals H4-H6 outputted to the switching elements Q4-Q6 ifcurrent detected by the motor-current detecting circuit 71 becomeslarger than the target current It. With this construction, currentlarger than the target current It is prevented from flowing through themotor 5, thereby preventing overcurrent from flowing through the motor5. Further, because a possibility of stop of the motor 5 due toovercurrent decreases, a smooth operation can be ensured. Further, itbecomes possible to protect the inverter circuit 8 vulnerable toovercurrent.

Here, the above-mentioned control performed by the arithmetic section 78will be described in detail while referring to FIG. 15. FIG. 15 is aflowchart of the voltage control according to the third embodiment. Thisflowchart is started when the trigger switch 3 is turned on.

First, the arithmetic section 78 obtains current I flowing through themotor 5 from the motor-current detecting circuit 71 (S201), anddetermines whether the current I is larger than the overcurrentthreshold Ith (S202).

If the current I is larger than the overcurrent threshold Ith (S202:Yes), the arithmetic section 78 sets the target duty Dt of the PWMsignals H4-H6 to 0%, thereby stopping supply of electric power to themotor 5 (S203). With this operation, overcurrent is prevented fromflowing through the motor 5.

On the other hand, if the current I is less than or equal to theovercurrent threshold Ith (S202: No), the arithmetic section 78 thendetermines whether the current I is larger than the target current It(S204).

If the current I is less than or equal to the target current It (S204:No), the arithmetic section 78 sets (increases) the target duty Dt forincreasing the current I to the target current It (S205) and returns toS201.

Specifically, the arithmetic section 78 set the target duty Dt based onthe following Equation (1): Dt=(It−I)×P+D (P is a feedback gain, and Dis a current duty), and increases the duty by Da % toward the targetduty Dt. By increasing the duty by Da % in this way, an excessive inrushcurrent can be prevented from flowing through the motor 5.

On the other hand, if the current I is larger than the target current It(S204: Yes), the arithmetic section 78 decreases the target duty Dt todecrease the target current It (S205) and returns to S201.

In this way, in the electric power tool 1C according to the thirdembodiment, if the current I flowing through the motor 5 is larger thanthe target current It, the target duty Dt is decreased. Thus, becausecurrent flowing through the motor 5 is smaller than the target currentIt, overcurrent can be prevented from flowing through the motor 5.Further, because a possibility of stop of the motor 5 due to overcurrentis decreased, a smooth operation can be ensured. Further, it becomespossible to protect the inverter circuit 8 vulnerable to overcurrent.

Note that, in the above embodiment, the target duty Dt is decreased at aconstant rate (Da %) if the current I is larger than the target currentIt. However, the decreasing rate may be changed in accordance with thecurrent I.

Further, in the above embodiment, supply of voltage to the motor 5 isstopped if the current I is larger than the overcurrent threshold Ith.However, supply of voltage to the motor 5 may be stopped if the currentI is larger than the target current It and is less than or equal to theovercurrent threshold Ith for a preset period or longer. In this case,the period may be changed depending on vulnerability of the motor 5 andthe inverter circuit 8 to overcurrent.

Next, an electric power tool 1D according to a fourth embodiment of theinvention will be described while referring to FIGS. 16 through 18. Theelectric power tool 1D has an identical circuit configuration (FIG. 1)as the electric power tool 1A according to the first embodiment.Therefore, the descriptions of the circuit configuration are omitted.

If the same voltage is supplied to the motor 5 in a case where therotational speed of the motor 5 is low and in a case where therotational speed of the motor 5 is high, larger current flows throughthe motor 5 in the case where the rotational speed is low. On the otherhand, change in the target duty Dt takes some time to be reflected in acurrent value. Accordingly, when the rotational speed of the motor 5 islow, even if the control according to the third embodiment is performed,there is a possibility that the control cannot follow and overcurrentflows through the motor 5.

Hence, in the present embodiment, as shown in FIG. 16, the target dutyDt is changed in accordance with the rotational speed of the motor 5.Specifically, the target duty Dt is set to a small value while therotational speed of the motor 5 is low, so that large voltage is notsupplied to the motor 5. With this operation, as shown in FIG. 17, whilethe rotational speed of the motor 5 is low, large current can beprevented from flowing through the motor 5. Hence, overcurrent throughthe motor 5 can be prevented appropriately.

Next, a control according to the present embodiment will be describedwhile referring to FIG. 18. FIG. 18 is a flowchart of the voltagecontrol according to the present embodiment. This flowchart starts whenthe trigger switch 3 is turned on. Note that steps S301-S303 areidentical to steps S201-S203 in FIG. 15, and thus descriptions areomitted.

If the current I is less than or equal to the overcurrent threshold Ith(S302: No), the arithmetic section 78 obtains rotational speed N of themotor 5 from the motor-rotational-speed detecting circuit 77 (S304).Then, the arithmetic section 78 sets, based on the rotational speed N,the target current It and the target duty Dt for increasing the currentI to the target current It (S305), and returns to S301. In the presentembodiment, as shown in FIG. 16, the target duty Dt is increasedproportionally to 100% when the rotational speed is 0 rpm to a presetrpm, and is fixed at 100% when the rotational speed is higher than thepreset rpm.

In this way, in the electric power tool 1D according to the fourthembodiment, the target duty Dt is changed in accordance with therotational speed of the motor 5. With this operation, while therotational speed of the motor 5 is low, large voltage is not supplied tothe motor 5. Hence, overcurrent can be prevented appropriately fromflowing through the motor 5.

Next, an electric power tool 1E according to a fifth embodiment of theinvention will be described while referring to FIGS. 19 through 21. Theelectric power tool 1D has an identical circuit configuration (FIG. 1)as the electric power tool 1A according to the first embodiment.Therefore, the descriptions of the circuit configuration are omitted.

In the first embodiment, the smoothing capacitor 23 having smallcapacity is used. Especially, when the capacity is less than or equal to10 uF (microfarad), pulsation voltage including ripples can be outputtedfrom the smoothing capacitor 23.

If the control according to the third embodiment is performed with thesmoothing capacitor 23 having small capacity, as shown in FIG. 19, thecurrent I starts decreasing after the current I becomes larger than thetarget current It.

However, in the control according to the third, the target duty Dt isincreased immediately after the current I decreases to a value less thanequal to the target current It. Therefore, as shown in FIG. 19, even ifthe current I is decreases to a value less than or equal to the targetcurrent It in one ripple, the current I exceeds the target current It innext ripple again. In other words, current exceeding the target currentIt flows through the motor 5 at each cycle of AC (alternate current). Asthe result, the motor 5 can be stopped due to overcurrent, or, at least,unnecessary heat is generated in the motor 5.

Hence, as shown in FIG. 20, the electric power tool 1E according to thepresent embodiment determines whether or not a peak current Ip is largerthan the target current It, reduces the target duty Dt when the peakcurrent Ip is larger than the target current It, keeps the decreasedduty Dt until a next peak current Ip is detected even if the current Idecreases to a value less than or equal to the target current It, andincreases the duty Dt stepwise if the peak current Ip is smaller thanthe target current It. With this operation, current exceeding the targetcurrent It is prevented from flowing through the motor 5 at each cycleof AC.

Note that a capacitor of 0.47 uF (microfarad) is used in the presentembodiment. If such capacitor is used, large pulsation voltage includinglarge ripples can be generated. For example, if a ripple is larger thanor equal to 70%, it can be said that the large pulsation is generated.The size of ripple is denoted by (dV/V*)×100% (V* is a maximum voltageinputted into the electric power tool 1E, and dV is a rate of change ofvoltage).

Here, a control according to the present embodiment will be described indetail while referring to FIG. 21. FIG. 21 is a flowchart of the voltagecontrol according to the present embodiment. This flowchart starts whenthe trigger switch 3 is turned on. Note that steps S401-S403 areidentical to steps S201-S203 in FIG. 15, and thus descriptions areomitted.

If the current I(t) is less than or equal to the overcurrent thresholdIth (S402: No), then the arithmetic section 78 determines whether thecurrent I(t) is smaller than a previous current I(t−1) (S404).

If the current I(t) is larger than or equal to the previous currentI(t−1) (S404: No), the arithmetic section 78 stores the current I(t) asthe previous current I(t−1) (S405), and returns to S401.

On the other hand, if the current I(t) is smaller than the previouscurrent I(t−1) (S404: Yes), the arithmetic section 78 specifies theprevious current I(t−1) as the peak current Ip (S406). Note that, in thepresent embodiment, the current I(t) is detected in a sampling periodsuch that a value sufficiently close to the actual peak current can bedetected.

Next, the arithmetic section 78 determines whether the peak current Ipis larger than the target current It (S407).

If the peak current Ip is less than or equal to the target current It(S407: No), the arithmetic section 78 sets the target duty Dt forincreasing the peak current Ip to the target current It (S408), andreturns to S401.

On the other hand, if the peak current Ip is larger than the targetcurrent It (S407: Yes), the arithmetic section 78 decreases the targetduty Dt to decrease the target current It (S409), and then returns toS401.

As described above, the electric power tool 1E according to the presentembodiment determines whether or not a peak current Ip is larger thanthe target current It, reduces the target duty Dt when the peak currentIp is larger than the target current It, keeps the decreased duty Dtuntil a next peak current Ip is detected even if the current I decreasesto a value less than or equal to the target current It, and increasesthe duty Dt stepwise if the peak current Ip is smaller than the targetcurrent It. With this operation, current exceeding the target current Itis prevented from flowing through the motor 5 at each cycle of AC.

Next, an electric power tool 1F according to a sixth embodiment of theinvention will be described while referring to FIGS. 22 and 23. Theelectric power tool 1F has an identical circuit configuration (FIG. 1)as the electric power tool 1A according to the first embodiment.Therefore, the descriptions of the circuit configuration are omitted.

In the sixth embodiment, the third embodiment and the fourth embodimentare implemented concurrently. Specifically, the target duty Dt ischanged in accordance with the rotational speed of the motor 5, andthen, if the current I is larger than the target current It, the targetduty Dt is reduced.

In this case, as shown in FIG. 22, the arithmetic section 78 sets thetarget duty Dt such that large voltage is not supplied to the motor 5while the rotational speed of the motor 5 is low, and fixes the duty at100% after the rotational speed of the motor 5 becomes larger than orequal to a preset value. After the duty is fixed at 100%, the arithmeticsection 78 decreases the target duty Dt if the current I becomes largerthan the target current It.

Here, a control according to the sixth embodiment will be described indetail while referring to FIG. 23. FIG. 23 is a flowchart of the voltagecontrol according to the sixth embodiment. This flowchart starts whenthe trigger switch 3 is turned on.

First, the arithmetic section 78 obtains the current I flowing throughthe motor 5 from the motor-current detecting circuit 71 (S501), anddetermines whether the current I is larger than the overcurrentthreshold Ith (S502).

If the current I is larger than the overcurrent threshold Ith (S502:Yes), the arithmetic section 78 sets the target duty Dt of the PWMsignals H4, H5, and H6 to 0%, thereby stopping supply of electric powerto the motor 5 (S503).

On the other hand, the current I is less than or equal to theovercurrent threshold Ith (S502: No), the arithmetic section 78 obtainsthe rotational speed N of the motor 5 from the motor-rotational-speeddetecting circuit 77 (S504) and sets the target current It and thetarget Dt based on the rotational speed N (S505).

Next, the arithmetic section 78 determines whether the current I islarger than the target current It set in S505 (S506).

If the current I is less than or equal to the target current It (S506:No), the arithmetic section 78 increases the target duty Dt (S507), andreturns to S501.

On the other hand, if the current I is larger than the target current It(S506: Yes), the arithmetic section 78 decreases the target duty Dt(S508), and then returns to S501.

In this way, by implementing the third embodiment and the fourthembodiment concurrently, overcurrent can be prevented more effectivelyfrom flowing through the motor 5.

Note that, in the above embodiment, the target duty Dt is decreased at aconstant decreasing rate (Da %) if the current I is larger than thetarget current It. However, the decreasing rate may be changed inaccordance with the current I.

Further, in the above embodiment, supply of voltage to the motor 5 isstopped if the current I is larger than the overcurrent threshold Ith.However, supply of voltage to the motor 5 may be stopped if the currentI is larger than the target current It and is less than or equal to theovercurrent threshold Ith for a preset period or longer. In this case,the preset period may be changed depending on vulnerability of the motor5 and the inverter circuit 8 to overcurrent.

While the electric power tool of the invention has been described indetail with reference to the above embodiments thereof, it would beapparent to those skilled in the art that various changes andmodifications may be made therein without departing from the scope ofthe claims.

For example, if the electric power tools 1A-F are drivers, a lockdetection may be performed at the end of a driving operation. In thiscase, for example, the lock detection could be performed (1) if therotational speed N is less than or equal to a preset value, (2) if therotational speed N is less than or equal to a preset value, and thecurrent I is larger than or equal to a preset value, or (3) if thecurrent I continues being larger than or equal to a preset value for apreset period or longer.

Further, any two or more of the electric power tools 1A-1F can bearbitrarily combined with one another.

-   -   1A-1E Electric Power Tool    -   5 Motor    -   8 Inverter Circuit    -   10 Rectifier Circuit    -   11 Smoothing Capacitor

What is claimed is:
 1. An electric power tool comprising: a brushless motor including a stator and a rotor, the stator having a plurality of windings, the rotor being rotatable relative to the stator, an induced voltage being generated from the plurality of windings upon rotations of the rotor, the induced voltage having a voltage level determined depending upon number of rotations of the rotor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to produce from the rectified voltage a pulsating voltage in which ripples remain; an inverter circuit configured to sequentially switch the plurality of windings for energization by a capacitor voltage developed across the smoothing capacitor; a receiving unit configured to receive a drive instruction for driving the brushless motor by a user; and a control unit configured to control the inverter circuit, wherein the smoothing capacitor has such a capacity that a first period of time for which a current flows through the brushless motor and a second period of time for which the current does not flow through the brushless motor alternately take place, the current flowing through the brushless motor for the first period of time being caused by the capacitor voltage exceeding the induced voltage resulting from a variation in the capacitor voltage accompanying a variation in the rectified voltage, the current not flowing through the brushless motor for the second period of time being caused by a balance of the capacitor voltage with the induced voltage, wherein the control unit is configured to control the inverter circuit such that the inverter circuit performs the sequential switching during both the first period of time and the second period of time insofar as the drive instruction is being received at the receiving unit, and wherein the rectifier circuit and the smoothing capacitor are interiorly provided.
 2. An electric power tool comprising: a brushless motor including a stator and a rotor, the stator having a plurality of windings, the rotor being rotatable relative to the stator, an induced voltage being generated from the plurality of windings upon rotations of the rotor, the induced voltage having a voltage level determined depending upon number of rotations of the rotor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to produce from the rectified voltage a pulsating voltage in which ripples remain; an inverter circuit configured to sequentially switch the plurality of windings for energization by a capacitor voltage developed across the smoothing capacitor; a receiving unit configured to receive a drive instruction for driving the brushless motor by a user; and a control unit configured to control the inverter circuit, wherein the smoothing capacitor has such a capacity that a first period of time for which a current flows through the brushless motor and a second period of time for which the current does not flow through the brushless motor alternately take place, the current flowing through the brushless motor for the first period of time being caused by the capacitor voltage exceeding the induced voltage resulting from a fluctuation of the capacitor voltage accompanying a fluctuation of the rectified voltage, the current not flowing through the brushless motor for the second period of time being caused by a balance of the capacitor voltage with the induced voltage, wherein the control unit is configured to control the inverter circuit such that the inverter circuit performs the sequential switching during both the first period of time and the second period of time insofar as the drive instruction is being received at the receiving unit, and wherein the rectifier circuit and the smoothing capacitor are interiorly provided.
 3. The electric power tool according to claim 1 or 2, wherein the control unit is further configured to control the inverter circuit to halt the sequential switching when the current flowing through the brushless motor exceeds an overcurrent threshold value regardless of the drive instruction being received at the receiving unit. 